After initial hot rolling, aluminum base alloy strip and other metal strips are conventionally cold rolled with a lubricant of petroleum solvent (e.g., kerosene or normal paraffin or blends thereof) with minor additions (usually 3 or 4 percent by weight) of "natural" additives (e.g., fatty acids, esters, peanut oil or palm oil) to control viscosity, to inhibit rust and other oxidation, and to resist extreme pressure resistant materials. These conventional lubricants are used for general purpose rolling and also for the rolling of metal strips for ultimate use in food packaging.
Such cold rolling mills also require lubrication for their mechanical parts, such as gearing, and for the pressure systems of hydraulic components, such as those which press down and lift up the upper set of rolls. Such parts lubricants are referred to herein as "mechanical lubricants". Where the rolled strip is for use in food packaging, regulations prohibit use of any quantity of certain materials in lubricants applied to strip during rolling and any mechanical lubricants which might come in contact with the strip, if any detectable level of them remains on the rolled strip. In view of that requirement, it is generally customary, in the event of an inadvertent spill of contaminating mechanical lubricant into the rolling oil, to replace the rolling oil promptly and thereby minimize the chance of finding a detectable level on the rolled strip.
Polyalkylene glycol has long been known as a lubricant for various uses, and in recent years has been used increasingly to lubricate mechanical parts of mills for cold rolling aluminum strip, subject to the no detectable level requirements of 21 CFR 178.3570. More specifically, 100% polyalkylene glycol has been used to lubricate roll bearings, and 25 to 75% polyalkylene glycol has been blended with petroleum solvent to serve as the hydraulic fluid for operating hydraulic cylinders, such as those which press the rolls together.